"Firefox 7 uses less memory than Firefox 6 (and 5 and 4): often 20 percent to 30 percent less, and sometimes as much as 50 percent less," Nethercote said in a blog post Tuesday. "This means that Firefox 7 is faster (sometimes drastically so) and less likely to crash, particularly if you have many websites open at once and/or keep Firefox running for a long time between restarts."

Firefox has long been criticized for using large amounts of RAM and for not releasing memory when tabs are closed, practices that can degrade the browser's performance, or in extreme cases, cause it to crash or lock up.

Mozilla has tried to stop the leaks before. In 2008, a pair of company engineers claimed that work done on the then-under-construction Firefox 3 had paid off, with improved memory-handling compared to earlier versions and rivals.

Nethercote acknowledged Firefox's reputation as a "memory hog," and noted that some versions had used memory more efficiently than others, applauding Firefox 3, 3.5 and 3.6.

"But Firefox 4 regressed again, partly due to a large number of new features (not all of which were maximally efficient in their first iteration), and partly due to some over-aggressive tuning of heuristics relating to JavaScript garbage collection and image decoding," Nethercote said.

Nethercote cited tests that Mozilla and others had conducted with Firefox 7 that showed it used less memory than its predecessors and released unused memory more reliably when tabs were closed or the browser went idle.

"The reduced memory usage should also result in fewer crashes and aborts on Windows, where Firefox is built as a 32-bit application and so is typically restricted to only 2GB of virtual memory," Nethercote said.

Firefox 7 is currently in the "Aurora" channel, and will shift to a more reliable beta build on or shortly after next Tuesday, Aug. 16. If Mozilla maintains its rapid-release schedule, which results in a new edition every six weeks, the final version of Firefox 7 will ship Sept. 27.